Oryzomyini. Named as a subgenus of Oryzomys and either retained as such (Cabrera, 1961; Ellerman, 1941; Osgood, 1933a) or placed in synonymy with Oligoryzomys (Gyldenstolpe, 1932; Tate, 1932e; Thomas, 1926). Junior synonymy of Thallomyscus established by Osgood (1933a). Raised to genus by Carleton and Musser (1984) and later revised by them (1989). Cladistically primitive member of Oryzomyini, sharing certain morphological traits with Oligoryzomys (Carleton and Musser, 1989; Carleton and Olson, 1999); sister genus to Neacomys according to gene sequence studies (Myers et al., 1995; Patton and da Silva, 1995; Smith and Patton, 1999) or to the NeacomysOligoryzomys clade according to allozymic analyses (Dickerman and Yates, 1995).